A network switch is a computer networking device that connects devices together on a computer network, using packet switching to forward data to a destination device. The network switch is generally a media access control (MAC) bridge. The MAC bridge is a multi-port network bridge processing and forwarding data at a data link layer. A network switch in a data link layer network generally uses a Spanning Tree Protocol (STP) or Rapid Spanning Tree Protocol (RSTP) to ensure a loop-free topology for a bridged Ethernet local area network (LAN).
However, the STP or another type of loop breaking protocol does not distinguish an internal network used inside an organization and another external network. In this way, a situation in which an erroneous connection of the external network causes a topology of the internal network to change may exist.